ScrollableDebouce

scrollable_debounce.dart

class ScrollableDebounce extends StatefulWidget {
  const ScrollableDebounce({
    Key? key,
    required this.controller,
    required this.onScroll,
    this.debounceTime = const Duration(milliseconds: 200),
    required this.child,
  }) : super(key: key);

  /// An object that can be used to control the position to which this scroll
  /// view is scrolled.
  final ScrollController controller;

  /// The time for debouncing scroll events.
  ///
  /// Default value is `Duration(milliseconds: 200)`.
  final Duration debounceTime;

  /// Callback on debounced scroll event.
  final void Function(ScrollPosition scrollPosition) onScroll;

  /// The widget below this widget in the tree.
  ///
  /// {@template flutter.widgets.ProxyWidget.child}
  /// This widget can only have one child. To lay out multiple children, let this
  /// widget's child be a widget such as [Row], [Column], or [Stack], which have a
  /// `children` property, and then provide the children to that widget.
  /// {@endtemplate}
  final Widget child;

  @override
  State<ScrollableDebounce> createState() => _ScrollableDebounceState();
}

class _ScrollableDebounceState extends State<ScrollableDebounce> {
  final _streamController = StreamController<ScrollPosition>.broadcast();
  late final StreamSubscription<ScrollPosition> _streamSubscription;

  @override
  void dispose() {
    widget.controller.removeListener(_onScroll);
    _streamSubscription.cancel();
    _streamController.close();
    super.dispose();
  }

  @override
  void initState() {
    super.initState();
    _streamSubscription = _streamController.stream
        .debounceTime(widget.debounceTime)
        .listen(widget.onScroll);
    widget.controller.addListener(_onScroll);
  }

  @override
  void didUpdateWidget(covariant ScrollableDebounce oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (widget.controller != oldWidget.controller) {
      widget.controller.addListener(_onScroll);
      oldWidget.controller.removeListener(_onScroll);
    }
  }

  @override
  Widget build(BuildContext context) {
    return widget.child;
  }

  void _onScroll() {
    if (widget.controller.hasClients) {
      _streamController.add(widget.controller.position);
    }
  }
}